With a commanding 12-point lead over Manchester City with just seven games left, that remains the case, with United poised to land the club's 20th league title and the 13th of Sir Alex Ferguson's glittering reign.

It's just as well United went on that remorseless 18-match unbeaten run between November and April and opened up such a formidable advantage over City, for it the gap between the two sides was any smaller, you sense United, in their peculiar current state, could blow it for the second season running.

As it is, United would appear to have a big enough lead, despite hosting Chelsea and travelling to Arsenal before the end of the season, to get the job done this time. But just two wins in their last six games is indicative of a side low on confidence and energy.

In his post-match interviews, Ferguson was bullish, claiming United were the better side and had controlled the second-half. It smacked of political spin, putting a positive sheen on what was an undeniable setback, and the United boss was fooling no-one but himself.

Robin van Persie's United goal drought stretched to 10 games, Wayne Rooney looked sluggish and reverted to type in the first-half with a two-footed lunge on James Milner and could consider himself fortunate to have only been shown a yellow card.

Not in their best form: Wayne Rooney, Robin van Persie and Michael Carrick (Image: PA)

Ryan Giggs was guilty of an indulgent back-heel that saw him lose possession in the move that led to City's opener and looked every one of his 39 years against City's more enterprising and energetic midfield, while Michael Carrick, such an elegant and influential presence in the middle for United this season, lacked his usual authority on the ball.

In contrast, Carlos Tevez brimmed with intent up front for City, Yaya Toure and Gareth Barry won their midfield duel with Carrick and Giggs, while Sergio Aguero's sublime cameo, capped by his wonderful solo winner, at least restored some pride for Mancini's side in what has been a difficult campaign.

Of course, United could afford the luxury of slipping up against City given they are so far in front, and can re-establish their 15 -point advantage this Sunday with victory at Stoke while Mancini's men slug it out with Chelsea at Wembley for a place in the FA Cup final.

But United must learn lessons from their latest defeat to City, their second in a row at Old Trafford following last season's 6-1 debacle.

Despite his pre-match claim that City simply could not live with United this season, given how high his players had raised the bar this season in response to losing the title last season, Ferguson will not be fooled by the huge lead his side have over their nearest rivals.

The title may be all but in the bag, but Ferguson knows that United will have to strengthen considerably this summer to maintain the domestic dominance they have re-asserted this season.

Ferguson knows City will not buy as poorly this summer as they did last year, when their failure to land Mancini's top targets and players of real substance, to build on last season's success, handicapped them from the start of their title defence.

Ferguson alluded to just that ahead of the derby, when he said: "Whether we can go on another run of three titles in a row, who's to say?

"The materials are there, but it's a hard league. If Jose [Mourinho] goes back to Chelsea, as they're talking about, you'd expect a big challenge from there.

Mourinho: Could he return and make it interesting next term? (Image: Getty)

"City have enough money to go out and buy another £200million worth of players. They're not going to go away, are they, with the money they've got.

"I think Arsenal will improve - there's some indication they're building a better squad than people think - and Tottenham have been progressing for a couple of years now."

Arguably the chief factor in United's enduring success under Ferguson over two decades, while other rivals have come and gone, has been his refusal to stand still and back in the afterglow of trophies and achievements.

Monday's derby defeat was a timely reminder that, although United may have done enough to wrest the title back from City, the noisy neighbours remain rivals to be feared, despite their travails this season, and are sure to put up a bigger fight next season.